// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/debug/debugger.h"

#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <memory>
#include <vector>

#include "base/macros.h"
#include "build/build_config.h"

#if defined(__GLIBCXX__)
#include <cxxabi.h>
#endif

#if defined(OS_MACOSX)
#include <AvailabilityMacros.h>
#endif

#if defined(OS_MACOSX) || defined(OS_BSD)
#include <sys/sysctl.h>
#endif

#if defined(OS_FREEBSD)
#include <sys/user.h>
#endif

#include <ostream>

#include "base/debug/alias.h"
#include "base/logging.h"
#include "base/posix/eintr_wrapper.h"
#include "base/strings/string_piece.h"

#if defined(USE_SYMBOLIZE)
#include "base/third_party/symbolize/symbolize.h"
#endif

#if defined(OS_ANDROID)
#include "base/threading/platform_thread.h"
#endif

namespace base {
namespace debug {

#if defined(OS_MACOSX) || defined(OS_BSD)

    // Based on Apple's recommended method as described in
    // http://developer.apple.com/qa/qa2004/qa1361.html
    bool BeingDebugged()
    {
        // NOTE: This code MUST be async-signal safe (it's used by in-process
        // stack dumping signal handler). NO malloc or stdio is allowed here.
        //
        // While some code used below may be async-signal unsafe, note how
        // the result is cached (see |is_set| and |being_debugged| static variables
        // right below). If this code is properly warmed-up early
        // in the start-up process, it should be safe to use later.

        // If the process is sandboxed then we can't use the sysctl, so cache the
        // value.
        static bool is_set = false;
        static bool being_debugged = false;

        if (is_set)
            return being_debugged;

        // Initialize mib, which tells sysctl what info we want.  In this case,
        // we're looking for information about a specific process ID.
        int mib[] = {
            CTL_KERN,
            KERN_PROC,
            KERN_PROC_PID,
            getpid()
#if defined(OS_OPENBSD)
                ,
            sizeof(struct kinfo_proc),
            0
#endif
        };

        // Caution: struct kinfo_proc is marked __APPLE_API_UNSTABLE.  The source and
        // binary interfaces may change.
        struct kinfo_proc info;
        size_t info_size = sizeof(info);

#if defined(OS_OPENBSD)
        if (sysctl(mib, arraysize(mib), NULL, &info_size, NULL, 0) < 0)
            return -1;

        mib[5] = (info_size / sizeof(struct kinfo_proc));
#endif

        int sysctl_result = sysctl(mib, arraysize(mib), &info, &info_size, NULL, 0);
        DCHECK_EQ(sysctl_result, 0);
        if (sysctl_result != 0) {
            is_set = true;
            being_debugged = false;
            return being_debugged;
        }

        // This process is being debugged if the P_TRACED flag is set.
        is_set = true;
#if defined(OS_FREEBSD)
        being_debugged = (info.ki_flag & P_TRACED) != 0;
#elif defined(OS_BSD)
        being_debugged = (info.p_flag & P_TRACED) != 0;
#else
        being_debugged = (info.kp_proc.p_flag & P_TRACED) != 0;
#endif
        return being_debugged;
    }

#elif defined(OS_LINUX) || defined(OS_ANDROID)

    // We can look in /proc/self/status for TracerPid.  We are likely used in crash
    // handling, so we are careful not to use the heap or have side effects.
    // Another option that is common is to try to ptrace yourself, but then we
    // can't detach without forking(), and that's not so great.
    // static
    bool BeingDebugged()
    {
        // NOTE: This code MUST be async-signal safe (it's used by in-process
        // stack dumping signal handler). NO malloc or stdio is allowed here.

        int status_fd = open("/proc/self/status", O_RDONLY);
        if (status_fd == -1)
            return false;

        // We assume our line will be in the first 1024 characters and that we can
        // read this much all at once.  In practice this will generally be true.
        // This simplifies and speeds up things considerably.
        char buf[1024];

        ssize_t num_read = HANDLE_EINTR(read(status_fd, buf, sizeof(buf)));
        if (IGNORE_EINTR(close(status_fd)) < 0)
            return false;

        if (num_read <= 0)
            return false;

        StringPiece status(buf, num_read);
        StringPiece tracer("TracerPid:\t");

        StringPiece::size_type pid_index = status.find(tracer);
        if (pid_index == StringPiece::npos)
            return false;

        // Our pid is 0 without a debugger, assume this for any pid starting with 0.
        pid_index += tracer.size();
        return pid_index < status.size() && status[pid_index] != '0';
    }

#else

    bool BeingDebugged()
    {
        NOTIMPLEMENTED();
        return false;
    }

#endif

    // We want to break into the debugger in Debug mode, and cause a crash dump in
    // Release mode. Breakpad behaves as follows:
    //
    // +-------+-----------------+-----------------+
    // | OS    | Dump on SIGTRAP | Dump on SIGABRT |
    // +-------+-----------------+-----------------+
    // | Linux |       N         |        Y        |
    // | Mac   |       Y         |        N        |
    // +-------+-----------------+-----------------+
    //
    // Thus we do the following:
    // Linux: Debug mode if a debugger is attached, send SIGTRAP; otherwise send
    //        SIGABRT
    // Mac: Always send SIGTRAP.

#if defined(ARCH_CPU_ARMEL)
#define DEBUG_BREAK_ASM() asm("bkpt 0")
#elif defined(ARCH_CPU_ARM64)
#define DEBUG_BREAK_ASM() asm("brk 0")
#elif defined(ARCH_CPU_MIPS_FAMILY)
#define DEBUG_BREAK_ASM() asm("break 2")
#elif defined(ARCH_CPU_X86_FAMILY)
#define DEBUG_BREAK_ASM() asm("int3")
#endif

#if defined(NDEBUG) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
#define DEBUG_BREAK() abort()
#elif defined(OS_NACL)
// The NaCl verifier doesn't let use use int3.  For now, we call abort().  We
// should ask for advice from some NaCl experts about the optimum thing here.
// http://code.google.com/p/nativeclient/issues/detail?id=645
#define DEBUG_BREAK() abort()
#elif !defined(OS_MACOSX)
    // Though Android has a "helpful" process called debuggerd to catch native
    // signals on the general assumption that they are fatal errors. If no debugger
    // is attached, we call abort since Breakpad needs SIGABRT to create a dump.
    // When debugger is attached, for ARM platform the bkpt instruction appears
    // to cause SIGBUS which is trapped by debuggerd, and we've had great
    // difficulty continuing in a debugger once we stop from SIG triggered by native
    // code, use GDB to set |go| to 1 to resume execution; for X86 platform, use
    // "int3" to setup breakpiont and raise SIGTRAP.
    //
    // On other POSIX architectures, except Mac OS X, we use the same logic to
    // ensure that breakpad creates a dump on crashes while it is still possible to
    // use a debugger.
    namespace {
        void DebugBreak()
        {
            if (!BeingDebugged()) {
                abort();
            } else {
#if defined(DEBUG_BREAK_ASM)
                DEBUG_BREAK_ASM();
#else
                volatile int go = 0;
                while (!go) {
                    base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(100));
                }
#endif
            }
        }
    } // namespace
#define DEBUG_BREAK() DebugBreak()
#elif defined(DEBUG_BREAK_ASM)
#define DEBUG_BREAK() DEBUG_BREAK_ASM()
#else
#error "Don't know how to debug break on this architecture/OS"
#endif

    void BreakDebugger()
    {
        // NOTE: This code MUST be async-signal safe (it's used by in-process
        // stack dumping signal handler). NO malloc or stdio is allowed here.

        // Linker's ICF feature may merge this function with other functions with the
        // same definition (e.g. any function whose sole job is to call abort()) and
        // it may confuse the crash report processing system. http://crbug.com/508489
        static int static_variable_to_make_this_function_unique = 0;
        base::debug::Alias(&static_variable_to_make_this_function_unique);

        DEBUG_BREAK();
#if defined(OS_ANDROID) && !defined(OFFICIAL_BUILD)
        // For Android development we always build release (debug builds are
        // unmanageably large), so the unofficial build is used for debugging. It is
        // helpful to be able to insert BreakDebugger() statements in the source,
        // attach the debugger, inspect the state of the program and then resume it by
        // setting the 'go' variable above.
#elif defined(NDEBUG)
        // Terminate the program after signaling the debug break.
        _exit(1);
#endif
    }

} // namespace debug
} // namespace base
